The present invention relates to a method and an apparatus for detecting defects of a tape which is usable to record and reproduce dictations.
In countries in Europe and America in particular, a central dictation system is extensively used in which a dictating machine is installed in a certain location and operated by remote control from one or more terminal units. The system allows messages which are dictated on the terminal units to be sent to the dictating machine to be recorded on a magnetic tape, which is loaded in the machine. Specifically, a plurality of messages are sequentially recorded on the tape on a time division basis. Hence, when a tape recorded meassages is to be reused for other dictations or immediately after the power source of the machine has been turned on, the machine is routinely initialized to make it ready for dictation, i.e., erasing previously recorded and no longer needed the messages while rewinding the tape at a high speed. During the initialization, as soon as the tape is rewound to reach beginning of tape (BOT), the machine is automatically brought into a stop mode. Thereafter, a person in charge of the machine depresses a clear button and, then, manipulates a deck selection switch adapted to select, for example, one of two decks turning it to a dictation mode. This completes the initialization to thereby render the machine prepared for dictation.
Whether or not the high-speed erasure has been completed to BOT of a tape has customarily been determined by simply sensing pulses which are generated by detecting the rotation of a reel, which serves to take up or supply the tape at the time of initialization. Specifically, when the apparance of such pulses has ceased, it is determined that the erasure has been completed to BOT. However, such a prior art decision system brings about a critical problem when a tape is broken to cut or jammed before the rewind for initialization. So long as the pulses mentioned above are derived from the rotation of the reel which is to take up the tape in the high-speed rewind (REW) mode, such a problem may be detected by monitoring the pulses generated from the takeup reel which never stops, thus the pulses continue to be present more than a predetermined period of time. However, when the system is designed to sense rotation of the other reel, usually a takeup reel in a playback or a recording mode, which supplies the tape in the REW mode, the system functions as an automatic stop control in either situations, i.e., the completion of the initialization with a normal tape or torn tape which does not rotate the other reel. In other words, the system cannot distinguish an abnormal tape from a normal "end of the tape" stop. This prevents the operator of the machine from noticing the abnormal tape, and may attempt to make dictations which never materialize.